/**
 * @file
 * SNMP message processing (RFC1157).
 */

/*
 * Copyright (c) 2006 Axon Digital Design B.V., The Netherlands.
 * Copyright (c) 2016 Elias Oenal.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * Author: Christiaan Simons <christiaan.simons@axon.tv>
 *         Martin Hentschel <info@cl-soft.de>
 *         Elias Oenal <lwip@eliasoenal.com>
 */

#include "lwip/apps/snmp_opts.h"

#if LWIP_SNMP /* don't build if not configured for use in lwipopts.h */

#include "snmp_msg.h"
#include "snmp_asn1.h"
#include "snmp_core_priv.h"
#include "lwip/ip_addr.h"
#include "lwip/stats.h"

#if LWIP_SNMP_V3
#include "lwip/apps/snmpv3.h"
#include "snmpv3_priv.h"
#ifdef LWIP_SNMPV3_INCLUDE_ENGINE
#include LWIP_SNMPV3_INCLUDE_ENGINE
#endif
#endif

#include <string.h>

/* public (non-static) constants */
/** SNMP community string */
const char *snmp_community = SNMP_COMMUNITY;
/** SNMP community string for write access */
const char *snmp_community_write = SNMP_COMMUNITY_WRITE;
/** SNMP community string for sending traps */
const char *snmp_community_trap = SNMP_COMMUNITY_TRAP;

snmp_write_callback_fct snmp_write_callback     = NULL;
void                   *snmp_write_callback_arg = NULL;

/**
 * @ingroup snmp_core
 * Returns current SNMP community string.
 * @return current SNMP community string
 */
const char *
snmp_get_community(void)
{
    return snmp_community;
}

/**
 * @ingroup snmp_core
 * Sets SNMP community string.
 * The string itself (its storage) must be valid throughout the whole life of
 * program (or until it is changed to sth else).
 *
 * @param community is a pointer to new community string
 */
void
snmp_set_community(const char *const community)
{
    LWIP_ASSERT("community string is too long!", strlen(community) <= SNMP_MAX_COMMUNITY_STR_LEN);
    snmp_community = community;
}

/**
 * @ingroup snmp_core
 * Returns current SNMP write-access community string.
 * @return current SNMP write-access community string
 */
const char *
snmp_get_community_write(void)
{
    return snmp_community_write;
}

/**
 * @ingroup snmp_traps
 * Returns current SNMP community string used for sending traps.
 * @return current SNMP community string used for sending traps
 */
const char *
snmp_get_community_trap(void)
{
    return snmp_community_trap;
}

/**
 * @ingroup snmp_core
 * Sets SNMP community string for write-access.
 * The string itself (its storage) must be valid throughout the whole life of
 * program (or until it is changed to sth else).
 *
 * @param community is a pointer to new write-access community string
 */
void
snmp_set_community_write(const char *const community)
{
    LWIP_ASSERT("community string must not be NULL", community != NULL);
    LWIP_ASSERT("community string is too long!", strlen(community) <= SNMP_MAX_COMMUNITY_STR_LEN);
    snmp_community_write = community;
}

/**
 * @ingroup snmp_traps
 * Sets SNMP community string used for sending traps.
 * The string itself (its storage) must be valid throughout the whole life of
 * program (or until it is changed to sth else).
 *
 * @param community is a pointer to new trap community string
 */
void
snmp_set_community_trap(const char *const community)
{
    LWIP_ASSERT("community string is too long!", strlen(community) <= SNMP_MAX_COMMUNITY_STR_LEN);
    snmp_community_trap = community;
}

/**
 * @ingroup snmp_core
 * Callback fired on every successful write access
 */
void
snmp_set_write_callback(snmp_write_callback_fct write_callback, void *callback_arg)
{
    snmp_write_callback     = write_callback;
    snmp_write_callback_arg = callback_arg;
}

/* ----------------------------------------------------------------------- */
/* forward declarations */
/* ----------------------------------------------------------------------- */

static err_t snmp_process_get_request(struct snmp_request *request);
static err_t snmp_process_getnext_request(struct snmp_request *request);
static err_t snmp_process_getbulk_request(struct snmp_request *request);
static err_t snmp_process_set_request(struct snmp_request *request);

static err_t snmp_parse_inbound_frame(struct snmp_request *request);
static err_t snmp_prepare_outbound_frame(struct snmp_request *request);
static err_t snmp_complete_outbound_frame(struct snmp_request *request);
static void snmp_execute_write_callbacks(struct snmp_request *request);


/* ----------------------------------------------------------------------- */
/* implementation */
/* ----------------------------------------------------------------------- */

void
snmp_receive(void *handle, struct pbuf *p, const ip_addr_t *source_ip, u16_t port)
{
    err_t err;
    struct snmp_request request;

    memset(&request, 0, sizeof(request));
    request.handle       = handle;
    request.source_ip    = source_ip;
    request.source_port  = port;
    request.inbound_pbuf = p;

    snmp_stats.inpkts++;

    err = snmp_parse_inbound_frame(&request);
    if (err == ERR_OK)
    {
        err = snmp_prepare_outbound_frame(&request);
        if (err == ERR_OK)
        {

            if (request.error_status == SNMP_ERR_NOERROR)
            {
                /* only process frame if we do not already have an error to return (e.g. all readonly) */
                if (request.request_type == SNMP_ASN1_CONTEXT_PDU_GET_REQ)
                {
                    err = snmp_process_get_request(&request);
                }
                else if (request.request_type == SNMP_ASN1_CONTEXT_PDU_GET_NEXT_REQ)
                {
                    err = snmp_process_getnext_request(&request);
                }
                else if (request.request_type == SNMP_ASN1_CONTEXT_PDU_GET_BULK_REQ)
                {
                    err = snmp_process_getbulk_request(&request);
                }
                else if (request.request_type == SNMP_ASN1_CONTEXT_PDU_SET_REQ)
                {
                    err = snmp_process_set_request(&request);
                }
            }

            if (err == ERR_OK)
            {
                err = snmp_complete_outbound_frame(&request);

                if (err == ERR_OK)
                {
                    err = snmp_sendto(request.handle, request.outbound_pbuf, request.source_ip, request.source_port);

                    if ((request.request_type == SNMP_ASN1_CONTEXT_PDU_SET_REQ)
                            && (request.error_status == SNMP_ERR_NOERROR)
                            && (snmp_write_callback != NULL))
                    {
                        /* raise write notification for all written objects */
                        snmp_execute_write_callbacks(&request);
                    }
                }
            }
        }

        if (request.outbound_pbuf != NULL)
        {
            pbuf_free(request.outbound_pbuf);
        }
    }
}

static u8_t
snmp_msg_getnext_validate_node_inst(struct snmp_node_instance *node_instance, void *validate_arg)
{
    if (((node_instance->access & SNMP_NODE_INSTANCE_ACCESS_READ) != SNMP_NODE_INSTANCE_ACCESS_READ) || (node_instance->get_value == NULL))
    {
        return SNMP_ERR_NOSUCHINSTANCE;
    }

    if ((node_instance->asn1_type == SNMP_ASN1_TYPE_COUNTER64) && (((struct snmp_request *)validate_arg)->version == SNMP_VERSION_1))
    {
        /* according to RFC 2089 skip Counter64 objects in GetNext requests from v1 clients */
        return SNMP_ERR_NOSUCHINSTANCE;
    }

    return SNMP_ERR_NOERROR;
}

static void
snmp_process_varbind(struct snmp_request *request, struct snmp_varbind *vb, u8_t get_next)
{
    err_t err;
    struct snmp_node_instance node_instance;
    memset(&node_instance, 0, sizeof(node_instance));

    if (get_next)
    {
        struct snmp_obj_id result_oid;
        request->error_status = snmp_get_next_node_instance_from_oid(vb->oid.id, vb->oid.len, snmp_msg_getnext_validate_node_inst, request,  &result_oid, &node_instance);

        if (request->error_status == SNMP_ERR_NOERROR)
        {
            snmp_oid_assign(&vb->oid, result_oid.id, result_oid.len);
        }
    }
    else
    {
        request->error_status = snmp_get_node_instance_from_oid(vb->oid.id, vb->oid.len, &node_instance);

        if (request->error_status == SNMP_ERR_NOERROR)
        {
            /* use 'getnext_validate' method for validation to avoid code duplication (some checks have to be executed here) */
            request->error_status = snmp_msg_getnext_validate_node_inst(&node_instance, request);

            if (request->error_status != SNMP_ERR_NOERROR)
            {
                if (node_instance.release_instance != NULL)
                {
                    node_instance.release_instance(&node_instance);
                }
            }
        }
    }

    if (request->error_status != SNMP_ERR_NOERROR)
    {
        if (request->error_status >= SNMP_VARBIND_EXCEPTION_OFFSET)
        {
            if ((request->version == SNMP_VERSION_2c) || request->version == SNMP_VERSION_3)
            {
                /* in SNMP v2c a varbind related exception is stored in varbind and not in frame header */
                vb->type = (SNMP_ASN1_CONTENTTYPE_PRIMITIVE | SNMP_ASN1_CLASS_CONTEXT | (request->error_status & SNMP_VARBIND_EXCEPTION_MASK));
                vb->value_len = 0;

                err = snmp_append_outbound_varbind(&(request->outbound_pbuf_stream), vb);
                if (err == ERR_OK)
                {
                    /* we stored the exception in varbind -> go on */
                    request->error_status = SNMP_ERR_NOERROR;
                }
                else if (err == ERR_BUF)
                {
                    request->error_status = SNMP_ERR_TOOBIG;
                }
                else
                {
                    request->error_status = SNMP_ERR_GENERROR;
                }
            }
        }
        else
        {
            /* according to RFC 1157/1905, all other errors only return genError */
            request->error_status = SNMP_ERR_GENERROR;
        }
    }
    else
    {
        s16_t len = node_instance.get_value(&node_instance, vb->value);
        vb->type = node_instance.asn1_type;

        if(len >= 0)
        {
            vb->value_len = (u16_t)len; /* cast is OK because we checked >= 0 above */

            LWIP_ASSERT("SNMP_MAX_VALUE_SIZE is configured too low", (vb->value_len & ~SNMP_GET_VALUE_RAW_DATA) <= SNMP_MAX_VALUE_SIZE);
            err = snmp_append_outbound_varbind(&request->outbound_pbuf_stream, vb);

            if (err == ERR_BUF)
            {
                request->error_status = SNMP_ERR_TOOBIG;
            }
            else if (err != ERR_OK)
            {
                request->error_status = SNMP_ERR_GENERROR;
            }
        }
        else
        {
            request->error_status = SNMP_ERR_GENERROR;
        }

        if (node_instance.release_instance != NULL)
        {
            node_instance.release_instance(&node_instance);
        }
    }
}


/**
 * Service an internal or external event for SNMP GET.
 *
 * @param request points to the associated message process state
 */
static err_t
snmp_process_get_request(struct snmp_request *request)
{
    snmp_vb_enumerator_err_t err;
    struct snmp_varbind vb;
    vb.value = request->value_buffer;

    LWIP_DEBUGF(SNMP_DEBUG, ("SNMP get request\n"));

    while (request->error_status == SNMP_ERR_NOERROR)
    {
        err = snmp_vb_enumerator_get_next(&request->inbound_varbind_enumerator, &vb);
        if (err == SNMP_VB_ENUMERATOR_ERR_OK)
        {
            if ((vb.type == SNMP_ASN1_TYPE_NULL) && (vb.value_len == 0))
            {
                snmp_process_varbind(request, &vb, 0);
            }
            else
            {
                request->error_status = SNMP_ERR_GENERROR;
            }
        }
        else if (err == SNMP_VB_ENUMERATOR_ERR_EOVB)
        {
            /* no more varbinds in request */
            break;
        }
        else if (err == SNMP_VB_ENUMERATOR_ERR_ASN1ERROR)
        {
            /* malformed ASN.1, don't answer */
            return ERR_ARG;
        }
        else
        {
            request->error_status = SNMP_ERR_GENERROR;
        }
    }

    return ERR_OK;
}

/**
 * Service an internal or external event for SNMP GET.
 *
 * @param request points to the associated message process state
 */
static err_t
snmp_process_getnext_request(struct snmp_request *request)
{
    snmp_vb_enumerator_err_t err;
    struct snmp_varbind vb;
    vb.value = request->value_buffer;

    LWIP_DEBUGF(SNMP_DEBUG, ("SNMP get-next request\n"));

    while (request->error_status == SNMP_ERR_NOERROR)
    {
        err = snmp_vb_enumerator_get_next(&request->inbound_varbind_enumerator, &vb);
        if (err == SNMP_VB_ENUMERATOR_ERR_OK)
        {
            if ((vb.type == SNMP_ASN1_TYPE_NULL) && (vb.value_len == 0))
            {
                snmp_process_varbind(request, &vb, 1);
            }
            else
            {
                request->error_status = SNMP_ERR_GENERROR;
            }
        }
        else if (err == SNMP_VB_ENUMERATOR_ERR_EOVB)
        {
            /* no more varbinds in request */
            break;
        }
        else if (err == SNMP_VB_ENUMERATOR_ERR_ASN1ERROR)
        {
            /* malformed ASN.1, don't answer */
            return ERR_ARG;
        }
        else
        {
            request->error_status = SNMP_ERR_GENERROR;
        }
    }

    return ERR_OK;
}

/**
 * Service an internal or external event for SNMP GETBULKT.
 *
 * @param request points to the associated message process state
 */
static err_t
snmp_process_getbulk_request(struct snmp_request *request)
{
    snmp_vb_enumerator_err_t err;
    s32_t non_repeaters     = request->non_repeaters;
    s32_t repetitions;
    u16_t repetition_offset = 0;
    struct snmp_varbind_enumerator repetition_varbind_enumerator;
    struct snmp_varbind vb;
    vb.value = request->value_buffer;

    if (SNMP_LWIP_GETBULK_MAX_REPETITIONS > 0)
    {
        repetitions = LWIP_MIN(request->max_repetitions, SNMP_LWIP_GETBULK_MAX_REPETITIONS);
    }
    else
    {
        repetitions = request->max_repetitions;
    }

    LWIP_DEBUGF(SNMP_DEBUG, ("SNMP get-bulk request\n"));

    /* process non repeaters and first repetition */
    while (request->error_status == SNMP_ERR_NOERROR)
    {
        if (non_repeaters == 0)
        {
            repetition_offset = request->outbound_pbuf_stream.offset;

            if (repetitions == 0)
            {
                /* do not resolve repeaters when repetitions is set to 0 */
                break;
            }
            repetitions--;
        }

        err = snmp_vb_enumerator_get_next(&request->inbound_varbind_enumerator, &vb);
        if (err == SNMP_VB_ENUMERATOR_ERR_EOVB)
        {
            /* no more varbinds in request */
            break;
        }
        else if (err == SNMP_VB_ENUMERATOR_ERR_ASN1ERROR)
        {
            /* malformed ASN.1, don't answer */
            return ERR_ARG;
        }
        else if ((err != SNMP_VB_ENUMERATOR_ERR_OK) || (vb.type != SNMP_ASN1_TYPE_NULL) || (vb.value_len != 0))
        {
            request->error_status = SNMP_ERR_GENERROR;
        }
        else
        {
            snmp_process_varbind(request, &vb, 1);
            non_repeaters--;
        }
    }

    /* process repetitions > 1 */
    while ((request->error_status == SNMP_ERR_NOERROR) && (repetitions > 0) && (request->outbound_pbuf_stream.offset != repetition_offset))
    {

        u8_t all_endofmibview = 1;

        snmp_vb_enumerator_init(&repetition_varbind_enumerator, request->outbound_pbuf, repetition_offset, request->outbound_pbuf_stream.offset - repetition_offset);
        repetition_offset = request->outbound_pbuf_stream.offset; /* for next loop */

        while (request->error_status == SNMP_ERR_NOERROR)
        {
            vb.value = NULL; /* do NOT decode value (we enumerate outbound buffer here, so all varbinds have values assigned) */
            err = snmp_vb_enumerator_get_next(&repetition_varbind_enumerator, &vb);
            if (err == SNMP_VB_ENUMERATOR_ERR_OK)
            {
                vb.value = request->value_buffer;
                snmp_process_varbind(request, &vb, 1);

                if (request->error_status != SNMP_ERR_NOERROR)
                {
                    /* already set correct error-index (here it cannot be taken from inbound varbind enumerator) */
                    request->error_index = request->non_repeaters + repetition_varbind_enumerator.varbind_count;
                }
                else if (vb.type != (SNMP_ASN1_CONTENTTYPE_PRIMITIVE | SNMP_ASN1_CLASS_CONTEXT | SNMP_ASN1_CONTEXT_VARBIND_END_OF_MIB_VIEW))
                {
                    all_endofmibview = 0;
                }
            }
            else if (err == SNMP_VB_ENUMERATOR_ERR_EOVB)
            {
                /* no more varbinds in request */
                break;
            }
            else
            {
                LWIP_DEBUGF(SNMP_DEBUG, ("Very strange, we cannot parse the varbind output that we created just before!"));
                request->error_status = SNMP_ERR_GENERROR;
                request->error_index  = request->non_repeaters + repetition_varbind_enumerator.varbind_count;
            }
        }

        if ((request->error_status == SNMP_ERR_NOERROR) && all_endofmibview)
        {
            /* stop when all varbinds in a loop return EndOfMibView */
            break;
        }

        repetitions--;
    }

    if (request->error_status == SNMP_ERR_TOOBIG)
    {
        /* for GetBulk it is ok, if not all requested variables fit into the response -> just return the varbinds added so far */
        request->error_status = SNMP_ERR_NOERROR;
    }

    return ERR_OK;
}

/**
 * Service an internal or external event for SNMP SET.
 *
 * @param request points to the associated message process state
 */
static err_t
snmp_process_set_request(struct snmp_request *request)
{
    snmp_vb_enumerator_err_t err;
    struct snmp_varbind vb;
    vb.value = request->value_buffer;

    LWIP_DEBUGF(SNMP_DEBUG, ("SNMP set request\n"));

    /* perform set test on all objects */
    while (request->error_status == SNMP_ERR_NOERROR)
    {
        err = snmp_vb_enumerator_get_next(&request->inbound_varbind_enumerator, &vb);
        if (err == SNMP_VB_ENUMERATOR_ERR_OK)
        {
            struct snmp_node_instance node_instance;
            memset(&node_instance, 0, sizeof(node_instance));

            request->error_status = snmp_get_node_instance_from_oid(vb.oid.id, vb.oid.len, &node_instance);
            if (request->error_status == SNMP_ERR_NOERROR)
            {
                if (node_instance.asn1_type != vb.type)
                {
                    request->error_status = SNMP_ERR_WRONGTYPE;
                }
                else if (((node_instance.access & SNMP_NODE_INSTANCE_ACCESS_WRITE) != SNMP_NODE_INSTANCE_ACCESS_WRITE) || (node_instance.set_value == NULL))
                {
                    request->error_status = SNMP_ERR_NOTWRITABLE;
                }
                else
                {
                    if (node_instance.set_test != NULL)
                    {
                        request->error_status = node_instance.set_test(&node_instance, vb.value_len, vb.value);
                    }
                }

                if (node_instance.release_instance != NULL)
                {
                    node_instance.release_instance(&node_instance);
                }
            }
        }
        else if (err == SNMP_VB_ENUMERATOR_ERR_EOVB)
        {
            /* no more varbinds in request */
            break;
        }
        else if (err == SNMP_VB_ENUMERATOR_ERR_INVALIDLENGTH)
        {
            request->error_status = SNMP_ERR_WRONGLENGTH;
        }
        else if (err == SNMP_VB_ENUMERATOR_ERR_ASN1ERROR)
        {
            /* malformed ASN.1, don't answer */
            return ERR_ARG;
        }
        else
        {
            request->error_status = SNMP_ERR_GENERROR;
        }
    }

    /* perform real set operation on all objects */
    if (request->error_status == SNMP_ERR_NOERROR)
    {
        snmp_vb_enumerator_init(&request->inbound_varbind_enumerator, request->inbound_pbuf, request->inbound_varbind_offset, request->inbound_varbind_len);
        while (request->error_status == SNMP_ERR_NOERROR)
        {
            err = snmp_vb_enumerator_get_next(&request->inbound_varbind_enumerator, &vb);
            if (err == SNMP_VB_ENUMERATOR_ERR_OK)
            {
                struct snmp_node_instance node_instance;
                memset(&node_instance, 0, sizeof(node_instance));
                request->error_status = snmp_get_node_instance_from_oid(vb.oid.id, vb.oid.len, &node_instance);
                if (request->error_status == SNMP_ERR_NOERROR)
                {
                    if (node_instance.set_value(&node_instance, vb.value_len, vb.value) != SNMP_ERR_NOERROR)
                    {
                        if (request->inbound_varbind_enumerator.varbind_count == 1)
                        {
                            request->error_status = SNMP_ERR_COMMITFAILED;
                        }
                        else
                        {
                            /* we cannot undo the set operations done so far */
                            request->error_status = SNMP_ERR_UNDOFAILED;
                        }
                    }

                    if (node_instance.release_instance != NULL)
                    {
                        node_instance.release_instance(&node_instance);
                    }
                }
            }
            else if (err == SNMP_VB_ENUMERATOR_ERR_EOVB)
            {
                /* no more varbinds in request */
                break;
            }
            else
            {
                /* first time enumerating varbinds work but second time not, although nothing should have changed in between ??? */
                request->error_status = SNMP_ERR_GENERROR;
            }
        }
    }

    return ERR_OK;
}

#define PARSE_EXEC(code, retValue) \
  if ((code) != ERR_OK) { \
    LWIP_DEBUGF(SNMP_DEBUG, ("Malformed ASN.1 detected.\n")); \
    snmp_stats.inasnparseerrs++; \
    return retValue; \
  }

#define PARSE_ASSERT(cond, retValue) \
  if (!(cond)) { \
    LWIP_DEBUGF(SNMP_DEBUG, ("SNMP parse assertion failed!: " # cond)); \
    snmp_stats.inasnparseerrs++; \
    return retValue; \
  }

#define BUILD_EXEC(code, retValue) \
  if ((code) != ERR_OK) { \
    LWIP_DEBUGF(SNMP_DEBUG, ("SNMP error during creation of outbound frame!: " # code)); \
    return retValue; \
  }

#define IF_PARSE_EXEC(code)   PARSE_EXEC(code, ERR_ARG)
#define IF_PARSE_ASSERT(code) PARSE_ASSERT(code, ERR_ARG)

/**
 * Checks and decodes incoming SNMP message header, logs header errors.
 *
 * @param request points to the current message request state return
 * @return
 * - ERR_OK SNMP header is sane and accepted
 * - ERR_VAL SNMP header is either malformed or rejected
 */
static err_t
snmp_parse_inbound_frame(struct snmp_request *request)
{
    struct snmp_pbuf_stream pbuf_stream;
    struct snmp_asn1_tlv tlv;
    s32_t parent_tlv_value_len;
    s32_t s32_value;
    err_t err;

    IF_PARSE_EXEC(snmp_pbuf_stream_init(&pbuf_stream, request->inbound_pbuf, 0, request->inbound_pbuf->tot_len));

    /* decode main container consisting of version, community and PDU */
    IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
    IF_PARSE_ASSERT((tlv.type == SNMP_ASN1_TYPE_SEQUENCE) && (tlv.value_len == pbuf_stream.length));
    parent_tlv_value_len = tlv.value_len;

    /* decode version */
    IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
    IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_INTEGER);
    parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
    IF_PARSE_ASSERT(parent_tlv_value_len > 0);

    IF_PARSE_EXEC(snmp_asn1_dec_s32t(&pbuf_stream, tlv.value_len, &s32_value));
    if ((s32_value != SNMP_VERSION_1) &&
            (s32_value != SNMP_VERSION_2c)
#if LWIP_SNMP_V3
            && (s32_value != SNMP_VERSION_3)
#endif
       )
    {
        /* unsupported SNMP version */
        snmp_stats.inbadversions++;
        return ERR_ARG;
    }
    request->version = (u8_t)s32_value;

#if LWIP_SNMP_V3
    if (request->version == SNMP_VERSION_3)
    {
        u16_t u16_value;
        u16_t inbound_msgAuthenticationParameters_offset;

        /* SNMPv3 doesn't use communities */
        /* @todo: Differentiate read/write access */
        strcpy((char *)request->community, snmp_community);
        request->community_strlen = (u16_t)strlen(snmp_community);

        /* RFC3414 globalData */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_SEQUENCE);
        parent_tlv_value_len -= SNMP_ASN1_TLV_HDR_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        /* decode msgID */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_INTEGER);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        IF_PARSE_EXEC(snmp_asn1_dec_s32t(&pbuf_stream, tlv.value_len, &s32_value));
        request->msg_id = s32_value;

        /* decode msgMaxSize */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_INTEGER);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        IF_PARSE_EXEC(snmp_asn1_dec_s32t(&pbuf_stream, tlv.value_len, &s32_value));
        request->msg_max_size = s32_value;

        /* decode msgFlags */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_OCTET_STRING);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        IF_PARSE_EXEC(snmp_asn1_dec_s32t(&pbuf_stream, tlv.value_len, &s32_value));
        request->msg_flags = (u8_t)s32_value;

        /* decode msgSecurityModel */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_INTEGER);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        IF_PARSE_EXEC(snmp_asn1_dec_s32t(&pbuf_stream, tlv.value_len, &s32_value));
        request->msg_security_model = s32_value;

        /* RFC3414 msgSecurityParameters
         * The User-based Security Model defines the contents of the OCTET
         * STRING as a SEQUENCE.
         *
         * We skip the protective dummy OCTET STRING header
         * to access the SEQUENCE header.
         */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_OCTET_STRING);
        parent_tlv_value_len -= SNMP_ASN1_TLV_HDR_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        /* msgSecurityParameters SEQUENCE header */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_SEQUENCE);
        parent_tlv_value_len -= SNMP_ASN1_TLV_HDR_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        /* decode msgAuthoritativeEngineID */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_OCTET_STRING);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        IF_PARSE_EXEC(snmp_asn1_dec_raw(&pbuf_stream, tlv.value_len, request->msg_authoritative_engine_id,
                                        &u16_value, SNMP_V3_MAX_ENGINE_ID_LENGTH));
        request->msg_authoritative_engine_id_len = (u8_t)u16_value;

        /* msgAuthoritativeEngineBoots */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_INTEGER);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);
        IF_PARSE_EXEC(snmp_asn1_dec_s32t(&pbuf_stream, tlv.value_len, &request->msg_authoritative_engine_boots));

        /* msgAuthoritativeEngineTime */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_INTEGER);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);
        IF_PARSE_EXEC(snmp_asn1_dec_s32t(&pbuf_stream, tlv.value_len, &request->msg_authoritative_engine_time));
        /* @todo: Implement time window checking */

        /* msgUserName */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_OCTET_STRING);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        IF_PARSE_EXEC(snmp_asn1_dec_raw(&pbuf_stream, tlv.value_len, request->msg_user_name,
                                        &u16_value, SNMP_V3_MAX_USER_LENGTH));
        request->msg_user_name_len = (u8_t)u16_value;
        /* @todo: Implement unknown user error response */
        IF_PARSE_EXEC(snmpv3_get_user((char *)request->msg_user_name, NULL, NULL, NULL, NULL));

        /* msgAuthenticationParameters */
        memset(request->msg_authentication_parameters, 0, SNMP_V3_MAX_AUTH_PARAM_LENGTH);
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_OCTET_STRING);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);
        /* Remember position */
        inbound_msgAuthenticationParameters_offset = pbuf_stream.offset;
        LWIP_UNUSED_ARG(inbound_msgAuthenticationParameters_offset);
        /* Read auth parameters */
        IF_PARSE_ASSERT(tlv.value_len <= SNMP_V3_MAX_AUTH_PARAM_LENGTH);
        IF_PARSE_EXEC(snmp_asn1_dec_raw(&pbuf_stream, tlv.value_len, request->msg_authentication_parameters,
                                        &u16_value, tlv.value_len));

#if LWIP_SNMP_V3_CRYPTO
        if (request->msg_flags & SNMP_V3_AUTH_FLAG)
        {
            const u8_t zero_arr[SNMP_V3_MAX_AUTH_PARAM_LENGTH] = { 0 };
            u8_t key[20];
            u8_t algo;
            u8_t hmac[LWIP_MAX(SNMP_V3_SHA_LEN, SNMP_V3_MD5_LEN)];
            struct snmp_pbuf_stream auth_stream;

            /* Rewind stream */
            IF_PARSE_EXEC(snmp_pbuf_stream_init(&pbuf_stream, request->inbound_pbuf, 0, request->inbound_pbuf->tot_len));
            IF_PARSE_EXEC(snmp_pbuf_stream_seek_abs(&pbuf_stream, inbound_msgAuthenticationParameters_offset));
            /* Set auth parameters to zero for verification */
            IF_PARSE_EXEC(snmp_asn1_enc_raw(&pbuf_stream, zero_arr, tlv.value_len));

            /* Verify authentication */
            IF_PARSE_EXEC(snmp_pbuf_stream_init(&auth_stream, request->inbound_pbuf, 0, request->inbound_pbuf->tot_len));

            IF_PARSE_EXEC(snmpv3_get_user((char *)request->msg_user_name, &algo, key, NULL, NULL));
            IF_PARSE_EXEC(snmpv3_auth(&auth_stream, request->inbound_pbuf->tot_len, key, algo, hmac));
            /* @todo: Implement error response */
            IF_PARSE_EXEC(memcmp(request->msg_authentication_parameters, hmac, SNMP_V3_MAX_AUTH_PARAM_LENGTH));
        }
#else
        /* Ungraceful exit if we encounter cryptography and don't support it.
         * @todo: Implement error response
         */
        IF_PARSE_ASSERT(!(request->msg_flags & (SNMP_V3_AUTH_FLAG | SNMP_V3_PRIV_FLAG)));
#endif

        /* msgPrivacyParameters */
        memset(request->msg_privacy_parameters, 0, SNMP_V3_MAX_PRIV_PARAM_LENGTH);
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_OCTET_STRING);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        IF_PARSE_EXEC(snmp_asn1_dec_raw(&pbuf_stream, tlv.value_len, request->msg_privacy_parameters,
                                        &u16_value, SNMP_V3_MAX_PRIV_PARAM_LENGTH));

#if LWIP_SNMP_V3_CRYPTO
        /* Decrypt message */
        if (request->msg_flags & SNMP_V3_PRIV_FLAG)
        {
            u8_t key[20];
            u8_t algo;

            IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
            IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_OCTET_STRING);
            parent_tlv_value_len -= SNMP_ASN1_TLV_HDR_LENGTH(tlv);
            IF_PARSE_ASSERT(parent_tlv_value_len > 0);

            IF_PARSE_EXEC(snmpv3_get_user((char *)request->msg_user_name, NULL, NULL, &algo, key));
            IF_PARSE_EXEC(snmpv3_crypt(&pbuf_stream, tlv.value_len, key,
                                       request->msg_privacy_parameters, request->msg_authoritative_engine_boots,
                                       request->msg_authoritative_engine_time, algo, SNMP_V3_PRIV_MODE_DECRYPT));
        }
#endif

        /* Scoped PDU
         * Encryption context
         */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_SEQUENCE);
        parent_tlv_value_len -= SNMP_ASN1_TLV_HDR_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        /* contextEngineID */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_OCTET_STRING);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        IF_PARSE_EXEC(snmp_asn1_dec_raw(&pbuf_stream, tlv.value_len, request->context_engine_id,
                                        &u16_value, SNMP_V3_MAX_ENGINE_ID_LENGTH));
        request->context_engine_id_len = (u8_t)u16_value;

        /* contextName */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_OCTET_STRING);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        IF_PARSE_EXEC(snmp_asn1_dec_raw(&pbuf_stream, tlv.value_len, request->context_name,
                                        &u16_value, SNMP_V3_MAX_ENGINE_ID_LENGTH));
        request->context_name_len = (u8_t)u16_value;
    }
    else
#endif
    {
        /* decode community */
        IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
        IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_OCTET_STRING);
        parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
        IF_PARSE_ASSERT(parent_tlv_value_len > 0);

        err = snmp_asn1_dec_raw(&pbuf_stream, tlv.value_len, request->community, &request->community_strlen, SNMP_MAX_COMMUNITY_STR_LEN);
        if (err == ERR_MEM)
        {
            /* community string does not fit in our buffer -> its too long -> its invalid */
            request->community_strlen = 0;
            snmp_pbuf_stream_seek(&pbuf_stream, tlv.value_len);
        }
        else
        {
            IF_PARSE_ASSERT(err == ERR_OK);
        }
        /* add zero terminator */
        request->community[request->community_strlen] = 0;
    }

    /* decode PDU type (next container level) */
    IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
    IF_PARSE_ASSERT(tlv.value_len <= pbuf_stream.length);
    request->inbound_padding_len = pbuf_stream.length - tlv.value_len;
    parent_tlv_value_len = tlv.value_len;

    /* validate PDU type */
    switch(tlv.type)
    {
    case (SNMP_ASN1_CLASS_CONTEXT | SNMP_ASN1_CONTENTTYPE_CONSTRUCTED | SNMP_ASN1_CONTEXT_PDU_GET_REQ):
        /* GetRequest PDU */
        snmp_stats.ingetrequests++;
        break;
    case (SNMP_ASN1_CLASS_CONTEXT | SNMP_ASN1_CONTENTTYPE_CONSTRUCTED | SNMP_ASN1_CONTEXT_PDU_GET_NEXT_REQ):
        /* GetNextRequest PDU */
        snmp_stats.ingetnexts++;
        break;
    case (SNMP_ASN1_CLASS_CONTEXT | SNMP_ASN1_CONTENTTYPE_CONSTRUCTED | SNMP_ASN1_CONTEXT_PDU_GET_BULK_REQ):
        /* GetBulkRequest PDU */
        if (request->version < SNMP_VERSION_2c)
        {
            /* RFC2089: invalid, drop packet */
            return ERR_ARG;
        }
        break;
    case (SNMP_ASN1_CLASS_CONTEXT | SNMP_ASN1_CONTENTTYPE_CONSTRUCTED | SNMP_ASN1_CONTEXT_PDU_SET_REQ):
        /* SetRequest PDU */
        snmp_stats.insetrequests++;
        break;
    default:
        /* unsupported input PDU for this agent (no parse error) */
        LWIP_DEBUGF(SNMP_DEBUG, ("Unknown/Invalid SNMP PDU type received: %d", tlv.type));
        \
        return ERR_ARG;
        break;
    }
    request->request_type = tlv.type & SNMP_ASN1_DATATYPE_MASK;

    /* validate community (do this after decoding PDU type because we don't want to increase 'inbadcommunitynames' for wrong frame types */
    if (request->community_strlen == 0)
    {
        /* community string was too long or really empty*/
        snmp_stats.inbadcommunitynames++;
        snmp_authfail_trap();
        return ERR_ARG;
    }
    else if (request->request_type == SNMP_ASN1_CONTEXT_PDU_SET_REQ)
    {
        if (snmp_community_write[0] == 0)
        {
            /* our write community is empty, that means all our objects are readonly */
            request->error_status = SNMP_ERR_NOTWRITABLE;
            request->error_index  = 1;
        }
        else if (strncmp(snmp_community_write, (const char *)request->community, SNMP_MAX_COMMUNITY_STR_LEN) != 0)
        {
            /* community name does not match */
            snmp_stats.inbadcommunitynames++;
            snmp_authfail_trap();
            return ERR_ARG;
        }
    }
    else
    {
        if (strncmp(snmp_community, (const char *)request->community, SNMP_MAX_COMMUNITY_STR_LEN) != 0)
        {
            /* community name does not match */
            snmp_stats.inbadcommunitynames++;
            snmp_authfail_trap();
            return ERR_ARG;
        }
    }

    /* decode request ID */
    IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
    IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_INTEGER);
    parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
    IF_PARSE_ASSERT(parent_tlv_value_len > 0);

    IF_PARSE_EXEC(snmp_asn1_dec_s32t(&pbuf_stream, tlv.value_len, &request->request_id));

    /* decode error status / non-repeaters */
    IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
    IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_INTEGER);
    parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
    IF_PARSE_ASSERT(parent_tlv_value_len > 0);

    if (request->request_type == SNMP_ASN1_CONTEXT_PDU_GET_BULK_REQ)
    {
        IF_PARSE_EXEC(snmp_asn1_dec_s32t(&pbuf_stream, tlv.value_len, &request->non_repeaters));
        if (request->non_repeaters < 0)
        {
            /* RFC 1905, 4.2.3 */
            request->non_repeaters = 0;
        }
    }
    else
    {
        /* only check valid value, don't touch 'request->error_status', maybe a response error status was already set to above; */
        IF_PARSE_EXEC(snmp_asn1_dec_s32t(&pbuf_stream, tlv.value_len, &s32_value));
        IF_PARSE_ASSERT(s32_value == SNMP_ERR_NOERROR);
    }

    /* decode error index / max-repetitions */
    IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
    IF_PARSE_ASSERT(tlv.type == SNMP_ASN1_TYPE_INTEGER);
    parent_tlv_value_len -= SNMP_ASN1_TLV_LENGTH(tlv);
    IF_PARSE_ASSERT(parent_tlv_value_len > 0);

    if (request->request_type == SNMP_ASN1_CONTEXT_PDU_GET_BULK_REQ)
    {
        IF_PARSE_EXEC(snmp_asn1_dec_s32t(&pbuf_stream, tlv.value_len, &request->max_repetitions));
        if (request->max_repetitions < 0)
        {
            /* RFC 1905, 4.2.3 */
            request->max_repetitions = 0;
        }
    }
    else
    {
        IF_PARSE_EXEC(snmp_asn1_dec_s32t(&pbuf_stream, tlv.value_len, &request->error_index));
        IF_PARSE_ASSERT(s32_value == 0);
    }

    /* decode varbind-list type (next container level) */
    IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));
    IF_PARSE_ASSERT((tlv.type == SNMP_ASN1_TYPE_SEQUENCE) && (tlv.value_len <= pbuf_stream.length));

    request->inbound_varbind_offset = pbuf_stream.offset;
    request->inbound_varbind_len    = pbuf_stream.length - request->inbound_padding_len;
    snmp_vb_enumerator_init(&(request->inbound_varbind_enumerator), request->inbound_pbuf, request->inbound_varbind_offset, request->inbound_varbind_len);

    return ERR_OK;
}

#define OF_BUILD_EXEC(code) BUILD_EXEC(code, ERR_ARG)

static err_t
snmp_prepare_outbound_frame(struct snmp_request *request)
{
    struct snmp_asn1_tlv tlv;
    struct snmp_pbuf_stream *pbuf_stream = &(request->outbound_pbuf_stream);

    /* try allocating pbuf(s) for maximum response size */
    request->outbound_pbuf = pbuf_alloc(PBUF_TRANSPORT, 1472, PBUF_RAM);
    if (request->outbound_pbuf == NULL)
    {
        return ERR_MEM;
    }

    snmp_pbuf_stream_init(pbuf_stream, request->outbound_pbuf, 0, request->outbound_pbuf->tot_len);

    /* 'Message' sequence */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 3, 0);
    OF_BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );

    /* version */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 0);
    snmp_asn1_enc_s32t_cnt(request->version, &tlv.value_len);
    OF_BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
    OF_BUILD_EXEC( snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, request->version) );

#if LWIP_SNMP_V3
    if (request->version < SNMP_VERSION_3)
    {
#endif
        /* community */
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 0, request->community_strlen);
        OF_BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
        OF_BUILD_EXEC( snmp_asn1_enc_raw(pbuf_stream, request->community, request->community_strlen) );
#if LWIP_SNMP_V3
    }
    else
    {
        const char *id;

        /* globalData */
        request->outbound_msg_global_data_offset = pbuf_stream->offset;
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 1, 0);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));

        /* msgID */
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 1);
        snmp_asn1_enc_s32t_cnt(request->msg_id, &tlv.value_len);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
        OF_BUILD_EXEC(snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, request->msg_id));

        /* msgMaxSize */
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 1);
        snmp_asn1_enc_s32t_cnt(request->msg_max_size, &tlv.value_len);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
        OF_BUILD_EXEC(snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, request->msg_max_size));

        /* msgFlags */
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 0, 1);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
        OF_BUILD_EXEC(snmp_asn1_enc_raw(pbuf_stream, &request->msg_flags, 1));

        /* msgSecurityModel */
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 1);
        snmp_asn1_enc_s32t_cnt(request->msg_security_model, &tlv.value_len);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
        OF_BUILD_EXEC(snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, request->msg_security_model));

        /* end of msgGlobalData */
        request->outbound_msg_global_data_end = pbuf_stream->offset;

        /* msgSecurityParameters */
        request->outbound_msg_security_parameters_str_offset = pbuf_stream->offset;
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 1, 0);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));

        request->outbound_msg_security_parameters_seq_offset = pbuf_stream->offset;
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 1, 0);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));

        /* msgAuthoritativeEngineID */
        snmpv3_get_engine_id(&id, &request->msg_authoritative_engine_id_len);
        MEMCPY(request->msg_authoritative_engine_id, id, request->msg_authoritative_engine_id_len);
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 0, request->msg_authoritative_engine_id_len);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
        OF_BUILD_EXEC(snmp_asn1_enc_raw(pbuf_stream, request->msg_authoritative_engine_id, request->msg_authoritative_engine_id_len));

        request->msg_authoritative_engine_time = snmpv3_get_engine_time();
        request->msg_authoritative_engine_boots = snmpv3_get_engine_boots();

        /* msgAuthoritativeEngineBoots */
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 0);
        snmp_asn1_enc_s32t_cnt(request->msg_authoritative_engine_boots, &tlv.value_len);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
        OF_BUILD_EXEC(snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, request->msg_authoritative_engine_boots));

        /* msgAuthoritativeEngineTime */
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 0);
        snmp_asn1_enc_s32t_cnt(request->msg_authoritative_engine_time, &tlv.value_len);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
        OF_BUILD_EXEC(snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, request->msg_authoritative_engine_time));

        /* msgUserName */
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 0, request->msg_user_name_len);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
        OF_BUILD_EXEC(snmp_asn1_enc_raw(pbuf_stream, request->msg_user_name, request->msg_user_name_len));

#if LWIP_SNMP_V3_CRYPTO
        /* msgAuthenticationParameters */
        if (request->msg_flags & SNMP_V3_AUTH_FLAG)
        {
            memset(request->msg_authentication_parameters, 0, SNMP_V3_MAX_AUTH_PARAM_LENGTH);
            request->outbound_msg_authentication_parameters_offset = pbuf_stream->offset;
            SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 1, SNMP_V3_MAX_AUTH_PARAM_LENGTH);
            OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
            OF_BUILD_EXEC(snmp_asn1_enc_raw(pbuf_stream, request->msg_authentication_parameters, SNMP_V3_MAX_AUTH_PARAM_LENGTH));
        }
        else
#endif
        {
            SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 0, 0);
            OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
        }

#if LWIP_SNMP_V3_CRYPTO
        /* msgPrivacyParameters */
        if (request->msg_flags & SNMP_V3_PRIV_FLAG)
        {
            snmpv3_build_priv_param(request->msg_privacy_parameters);

            SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 0, SNMP_V3_MAX_PRIV_PARAM_LENGTH);
            OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
            OF_BUILD_EXEC(snmp_asn1_enc_raw(pbuf_stream, request->msg_privacy_parameters, SNMP_V3_MAX_PRIV_PARAM_LENGTH));
        }
        else
#endif
        {
            SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 0, 0);
            OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
        }

        /* End of msgSecurityParameters, so we can calculate the length of this sequence later */
        request->outbound_msg_security_parameters_end = pbuf_stream->offset;

#if LWIP_SNMP_V3_CRYPTO
        /* For encryption we have to encapsulate the payload in an octet string */
        if (request->msg_flags & SNMP_V3_PRIV_FLAG)
        {
            request->outbound_scoped_pdu_string_offset = pbuf_stream->offset;
            SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 3, 0);
            OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
        }
#endif
        /* Scoped PDU
         * Encryption context
         */
        request->outbound_scoped_pdu_seq_offset = pbuf_stream->offset;
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 3, 0);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));

        /* contextEngineID */
        snmpv3_get_engine_id(&id, &request->context_engine_id_len);
        MEMCPY(request->context_engine_id, id, request->context_engine_id_len);
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 0, request->context_engine_id_len);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
        OF_BUILD_EXEC(snmp_asn1_enc_raw(pbuf_stream, request->context_engine_id, request->context_engine_id_len));

        /* contextName */
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 0, request->context_name_len);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
        OF_BUILD_EXEC(snmp_asn1_enc_raw(pbuf_stream, request->context_name, request->context_name_len));
    }
#endif

    /* 'PDU' sequence */
    request->outbound_pdu_offset = pbuf_stream->offset;
    SNMP_ASN1_SET_TLV_PARAMS(tlv, (SNMP_ASN1_CLASS_CONTEXT | SNMP_ASN1_CONTENTTYPE_CONSTRUCTED | SNMP_ASN1_CONTEXT_PDU_GET_RESP), 3, 0);
    OF_BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );

    /* request ID */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 0);
    snmp_asn1_enc_s32t_cnt(request->request_id, &tlv.value_len);
    OF_BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
    OF_BUILD_EXEC( snmp_asn1_enc_s32t(pbuf_stream, tlv.value_len, request->request_id) );

    /* error status */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 1);
    OF_BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
    request->outbound_error_status_offset = pbuf_stream->offset;
    OF_BUILD_EXEC( snmp_pbuf_stream_write(pbuf_stream, 0) );

    /* error index */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_INTEGER, 0, 1);
    OF_BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );
    request->outbound_error_index_offset = pbuf_stream->offset;
    OF_BUILD_EXEC( snmp_pbuf_stream_write(pbuf_stream, 0) );

    /* 'VarBindList' sequence */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 3, 0);
    OF_BUILD_EXEC( snmp_ans1_enc_tlv(pbuf_stream, &tlv) );

    request->outbound_varbind_offset = pbuf_stream->offset;

    return ERR_OK;
}

/** Calculate the length of a varbind list */
err_t
snmp_varbind_length(struct snmp_varbind *varbind, struct snmp_varbind_len *len)
{
    /* calculate required lengths */
    snmp_asn1_enc_oid_cnt(varbind->oid.id, varbind->oid.len, &len->oid_value_len);
    snmp_asn1_enc_length_cnt(len->oid_value_len, &len->oid_len_len);

    if (varbind->value_len == 0)
    {
        len->value_value_len = 0;
    }
    else if (varbind->value_len & SNMP_GET_VALUE_RAW_DATA)
    {
        len->value_value_len = varbind->value_len & (~SNMP_GET_VALUE_RAW_DATA);
    }
    else
    {
        switch (varbind->type)
        {
        case SNMP_ASN1_TYPE_INTEGER:
            if (varbind->value_len != sizeof (s32_t))
            {
                return ERR_VAL;
            }
            snmp_asn1_enc_s32t_cnt(*((s32_t *) varbind->value), &len->value_value_len);
            break;
        case SNMP_ASN1_TYPE_COUNTER:
        case SNMP_ASN1_TYPE_GAUGE:
        case SNMP_ASN1_TYPE_TIMETICKS:
            if (varbind->value_len != sizeof (u32_t))
            {
                return ERR_VAL;
            }
            snmp_asn1_enc_u32t_cnt(*((u32_t *) varbind->value), &len->value_value_len);
            break;
        case SNMP_ASN1_TYPE_OCTET_STRING:
        case SNMP_ASN1_TYPE_IPADDR:
        case SNMP_ASN1_TYPE_OPAQUE:
            len->value_value_len = varbind->value_len;
            break;
        case SNMP_ASN1_TYPE_NULL:
            if (varbind->value_len != 0)
            {
                return ERR_VAL;
            }
            len->value_value_len = 0;
            break;
        case SNMP_ASN1_TYPE_OBJECT_ID:
            if ((varbind->value_len & 0x03) != 0)
            {
                return ERR_VAL;
            }
            snmp_asn1_enc_oid_cnt((u32_t *) varbind->value, varbind->value_len >> 2, &len->value_value_len);
            break;
        case SNMP_ASN1_TYPE_COUNTER64:
            if (varbind->value_len != (2 * sizeof (u32_t)))
            {
                return ERR_VAL;
            }
            snmp_asn1_enc_u64t_cnt((u32_t *) varbind->value, &len->value_value_len);
            break;
        default:
            /* unsupported type */
            return ERR_VAL;
        }
    }
    snmp_asn1_enc_length_cnt(len->value_value_len, &len->value_len_len);

    len->vb_value_len = 1 + len->oid_len_len + len->oid_value_len + 1 + len->value_len_len + len->value_value_len;
    snmp_asn1_enc_length_cnt(len->vb_value_len, &len->vb_len_len);

    return ERR_OK;
}

#define OVB_BUILD_EXEC(code) BUILD_EXEC(code, ERR_ARG)

err_t
snmp_append_outbound_varbind(struct snmp_pbuf_stream *pbuf_stream, struct snmp_varbind *varbind)
{
    struct snmp_asn1_tlv tlv;
    struct snmp_varbind_len len;
    err_t err;

    err = snmp_varbind_length(varbind, &len);

    if (err != ERR_OK)
    {
        return err;
    }

    /* check length already before adding first data because in case of GetBulk,
     *  data added so far is returned and therefore no partial data shall be added
     */
    if ((1 + len.vb_len_len + len.vb_value_len) > pbuf_stream->length)
    {
        return ERR_BUF;
    }

    /* 'VarBind' sequence */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, len.vb_len_len, len.vb_value_len);
    OVB_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));

    /* VarBind OID */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OBJECT_ID, len.oid_len_len, len.oid_value_len);
    OVB_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));
    OVB_BUILD_EXEC(snmp_asn1_enc_oid(pbuf_stream, varbind->oid.id, varbind->oid.len));

    /* VarBind value */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, varbind->type, len.value_len_len, len.value_value_len);
    OVB_BUILD_EXEC(snmp_ans1_enc_tlv(pbuf_stream, &tlv));

    if (len.value_value_len > 0)
    {
        if (varbind->value_len & SNMP_GET_VALUE_RAW_DATA)
        {
            OVB_BUILD_EXEC(snmp_asn1_enc_raw(pbuf_stream, (u8_t *) varbind->value, len.value_value_len));
        }
        else
        {
            switch (varbind->type)
            {
            case SNMP_ASN1_TYPE_INTEGER:
                OVB_BUILD_EXEC(snmp_asn1_enc_s32t(pbuf_stream, len.value_value_len, *((s32_t *) varbind->value)));
                break;
            case SNMP_ASN1_TYPE_COUNTER:
            case SNMP_ASN1_TYPE_GAUGE:
            case SNMP_ASN1_TYPE_TIMETICKS:
                OVB_BUILD_EXEC(snmp_asn1_enc_u32t(pbuf_stream, len.value_value_len, *((u32_t *) varbind->value)));
                break;
            case SNMP_ASN1_TYPE_OCTET_STRING:
            case SNMP_ASN1_TYPE_IPADDR:
            case SNMP_ASN1_TYPE_OPAQUE:
                OVB_BUILD_EXEC(snmp_asn1_enc_raw(pbuf_stream, (u8_t *) varbind->value, len.value_value_len));
                len.value_value_len = varbind->value_len;
                break;
            case SNMP_ASN1_TYPE_OBJECT_ID:
                OVB_BUILD_EXEC(snmp_asn1_enc_oid(pbuf_stream, (u32_t *) varbind->value, varbind->value_len / sizeof (u32_t)));
                break;
            case SNMP_ASN1_TYPE_COUNTER64:
                OVB_BUILD_EXEC(snmp_asn1_enc_u64t(pbuf_stream, len.value_value_len, (u32_t *) varbind->value));
                break;
            default:
                LWIP_ASSERT("Unknown variable type", 0);
                break;
            }
        }
    }

    return ERR_OK;
}

static err_t
snmp_complete_outbound_frame(struct snmp_request *request)
{
    struct snmp_asn1_tlv tlv;
    u16_t frame_size;
    u8_t outbound_padding = 0;

    if (request->version == SNMP_VERSION_1)
    {
        if (request->error_status != SNMP_ERR_NOERROR)
        {
            /* map v2c error codes to v1 compliant error code (according to RFC 2089) */
            switch (request->error_status)
            {
            /* mapping of implementation specific "virtual" error codes
             * (during processing of frame we already stored them in error_status field,
             * so no need to check all varbinds here for those exceptions as suggested by RFC) */
            case SNMP_ERR_NOSUCHINSTANCE:
            case SNMP_ERR_NOSUCHOBJECT:
            case SNMP_ERR_ENDOFMIBVIEW:
                request->error_status = SNMP_ERR_NOSUCHNAME;
                break;
            /* mapping according to RFC */
            case SNMP_ERR_WRONGVALUE:
            case SNMP_ERR_WRONGENCODING:
            case SNMP_ERR_WRONGTYPE:
            case SNMP_ERR_WRONGLENGTH:
            case SNMP_ERR_INCONSISTENTVALUE:
                request->error_status = SNMP_ERR_BADVALUE;
                break;
            case SNMP_ERR_NOACCESS:
            case SNMP_ERR_NOTWRITABLE:
            case SNMP_ERR_NOCREATION:
            case SNMP_ERR_INCONSISTENTNAME:
            case SNMP_ERR_AUTHORIZATIONERROR:
                request->error_status = SNMP_ERR_NOSUCHNAME;
                break;
            case SNMP_ERR_RESOURCEUNAVAILABLE:
            case SNMP_ERR_COMMITFAILED:
            case SNMP_ERR_UNDOFAILED:
            default:
                request->error_status = SNMP_ERR_GENERROR;
                break;
            }
        }
    }
    else
    {
        if (request->request_type == SNMP_ASN1_CONTEXT_PDU_SET_REQ)
        {
            /* map error codes to according to RFC 1905 (4.2.5.  The SetRequest-PDU) return 'NotWritable' for unknown OIDs) */
            switch (request->error_status)
            {
            case SNMP_ERR_NOSUCHINSTANCE:
            case SNMP_ERR_NOSUCHOBJECT:
            case SNMP_ERR_ENDOFMIBVIEW:
                request->error_status = SNMP_ERR_NOTWRITABLE;
                break;
            default:
                break;
            }
        }

        if (request->error_status >= SNMP_VARBIND_EXCEPTION_OFFSET)
        {
            /* should never occur because v2 frames store exceptions directly inside varbinds and not as frame error_status */
            LWIP_DEBUGF(SNMP_DEBUG, ("snmp_complete_outbound_frame() > Found v2 request with varbind exception code stored as error status!\n"));
            return ERR_ARG;
        }
    }

    if ((request->error_status != SNMP_ERR_NOERROR) || (request->request_type == SNMP_ASN1_CONTEXT_PDU_SET_REQ))
    {
        /* all inbound vars are returned in response without any modification for error responses and successful set requests*/
        struct snmp_pbuf_stream inbound_stream;
        OF_BUILD_EXEC( snmp_pbuf_stream_init(&inbound_stream, request->inbound_pbuf, request->inbound_varbind_offset, request->inbound_varbind_len) );
        OF_BUILD_EXEC( snmp_pbuf_stream_init(&(request->outbound_pbuf_stream), request->outbound_pbuf, request->outbound_varbind_offset, request->outbound_pbuf->tot_len - request->outbound_varbind_offset) );
        snmp_pbuf_stream_writeto(&inbound_stream, &(request->outbound_pbuf_stream), 0);
    }

    frame_size = request->outbound_pbuf_stream.offset;

#if LWIP_SNMP_V3 && LWIP_SNMP_V3_CRYPTO
    /* Calculate padding for encryption */
    if (request->version == SNMP_VERSION_3 && (request->msg_flags & SNMP_V3_PRIV_FLAG))
    {
        u8_t i;
        outbound_padding = (8 - (u8_t)((frame_size - request->outbound_scoped_pdu_seq_offset) & 0x07)) & 0x07;
        for (i = 0; i < outbound_padding; i++)
        {
            snmp_pbuf_stream_write(&request->outbound_pbuf_stream, 0);
        }
    }
#endif

    /* complete missing length in 'Message' sequence ; 'Message' tlv is located at the beginning (offset 0) */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 3, frame_size + outbound_padding - 1 - 3); /* - type - length_len(fixed, see snmp_prepare_outbound_frame()) */
    OF_BUILD_EXEC( snmp_pbuf_stream_init(&(request->outbound_pbuf_stream), request->outbound_pbuf, 0, request->outbound_pbuf->tot_len) );
    OF_BUILD_EXEC( snmp_ans1_enc_tlv(&(request->outbound_pbuf_stream), &tlv) );

#if LWIP_SNMP_V3
    if (request->version == SNMP_VERSION_3)
    {
        /* complete missing length in 'globalData' sequence */
        /* - type - length_len(fixed, see snmp_prepare_outbound_frame()) */
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 1, request->outbound_msg_global_data_end
                                 - request->outbound_msg_global_data_offset - 1 - 1);
        OF_BUILD_EXEC(snmp_pbuf_stream_seek_abs(&(request->outbound_pbuf_stream), request->outbound_msg_global_data_offset));
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(&(request->outbound_pbuf_stream), &tlv));

        /* complete missing length in 'msgSecurityParameters' sequence */
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 1, request->outbound_msg_security_parameters_end
                                 - request->outbound_msg_security_parameters_str_offset - 1 - 1);
        OF_BUILD_EXEC(snmp_pbuf_stream_seek_abs(&(request->outbound_pbuf_stream), request->outbound_msg_security_parameters_str_offset));
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(&(request->outbound_pbuf_stream), &tlv));

        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 1, request->outbound_msg_security_parameters_end
                                 - request->outbound_msg_security_parameters_seq_offset - 1 - 1);
        OF_BUILD_EXEC(snmp_pbuf_stream_seek_abs(&(request->outbound_pbuf_stream), request->outbound_msg_security_parameters_seq_offset));
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(&(request->outbound_pbuf_stream), &tlv));

        /* complete missing length in scoped PDU sequence */
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 3, frame_size - request->outbound_scoped_pdu_seq_offset - 1 - 3);
        OF_BUILD_EXEC(snmp_pbuf_stream_seek_abs(&(request->outbound_pbuf_stream), request->outbound_scoped_pdu_seq_offset));
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(&(request->outbound_pbuf_stream), &tlv));
    }
#endif

    /* complete missing length in 'PDU' sequence */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, (SNMP_ASN1_CLASS_CONTEXT | SNMP_ASN1_CONTENTTYPE_CONSTRUCTED | SNMP_ASN1_CONTEXT_PDU_GET_RESP), 3,
                             frame_size - request->outbound_pdu_offset - 1 - 3); /* - type - length_len(fixed, see snmp_prepare_outbound_frame()) */
    OF_BUILD_EXEC( snmp_pbuf_stream_seek_abs(&(request->outbound_pbuf_stream), request->outbound_pdu_offset) );
    OF_BUILD_EXEC( snmp_ans1_enc_tlv(&(request->outbound_pbuf_stream), &tlv) );

    /* process and encode final error status */
    if (request->error_status != 0)
    {
        u16_t len;
        snmp_asn1_enc_s32t_cnt(request->error_status, &len);
        if (len != 1)
        {
            /* error, we only reserved one byte for it */
            return ERR_ARG;
        }
        OF_BUILD_EXEC( snmp_pbuf_stream_seek_abs(&(request->outbound_pbuf_stream), request->outbound_error_status_offset) );
        OF_BUILD_EXEC( snmp_asn1_enc_s32t(&(request->outbound_pbuf_stream), len, request->error_status) );

        /* for compatibility to v1, log statistics; in v2 (RFC 1907) these statistics are obsoleted */
        switch (request->error_status)
        {
        case SNMP_ERR_TOOBIG:
            snmp_stats.outtoobigs++;
            break;
        case SNMP_ERR_NOSUCHNAME:
            snmp_stats.outnosuchnames++;
            break;
        case SNMP_ERR_BADVALUE:
            snmp_stats.outbadvalues++;
            break;
        case SNMP_ERR_GENERROR:
        default:
            snmp_stats.outgenerrs++;
            break;
        }

        if (request->error_status == SNMP_ERR_TOOBIG)
        {
            request->error_index = 0; /* defined by RFC 1157 */
        }
        else if (request->error_index == 0)
        {
            /* set index to varbind where error occured (if not already set before, e.g. during GetBulk processing) */
            request->error_index = request->inbound_varbind_enumerator.varbind_count;
        }
    }
    else
    {
        if (request->request_type == SNMP_ASN1_CONTEXT_PDU_SET_REQ)
        {
            snmp_stats.intotalsetvars += request->inbound_varbind_enumerator.varbind_count;
        }
        else
        {
            snmp_stats.intotalreqvars += request->inbound_varbind_enumerator.varbind_count;
        }
    }

    /* encode final error index*/
    if (request->error_index != 0)
    {
        u16_t len;
        snmp_asn1_enc_s32t_cnt(request->error_index, &len);
        if (len != 1)
        {
            /* error, we only reserved one byte for it */
            return ERR_VAL;
        }
        OF_BUILD_EXEC( snmp_pbuf_stream_seek_abs(&(request->outbound_pbuf_stream), request->outbound_error_index_offset) );
        OF_BUILD_EXEC( snmp_asn1_enc_s32t(&(request->outbound_pbuf_stream), len, request->error_index) );
    }

    /* complete missing length in 'VarBindList' sequence ; 'VarBindList' tlv is located directly before varbind offset */
    SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_SEQUENCE, 3, frame_size - request->outbound_varbind_offset);
    OF_BUILD_EXEC( snmp_pbuf_stream_seek_abs(&(request->outbound_pbuf_stream), request->outbound_varbind_offset - 1 - 3) ); /* - type - length_len(fixed, see snmp_prepare_outbound_frame()) */
    OF_BUILD_EXEC( snmp_ans1_enc_tlv(&(request->outbound_pbuf_stream), &tlv) );

    /* Authenticate response */
#if LWIP_SNMP_V3 && LWIP_SNMP_V3_CRYPTO
    /* Encrypt response */
    if (request->version == SNMP_VERSION_3 && (request->msg_flags & SNMP_V3_PRIV_FLAG))
    {
        u8_t key[20];
        u8_t algo;

        /* complete missing length in PDU sequence */
        OF_BUILD_EXEC(snmp_pbuf_stream_init(&request->outbound_pbuf_stream, request->outbound_pbuf, 0, request->outbound_pbuf->tot_len));
        OF_BUILD_EXEC(snmp_pbuf_stream_seek_abs(&(request->outbound_pbuf_stream), request->outbound_scoped_pdu_string_offset));
        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 3, frame_size + outbound_padding
                                 - request->outbound_scoped_pdu_string_offset - 1 - 3);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(&(request->outbound_pbuf_stream), &tlv));

        OF_BUILD_EXEC(snmpv3_get_user((char *)request->msg_user_name, NULL, NULL, &algo, key));

        OF_BUILD_EXEC(snmpv3_crypt(&request->outbound_pbuf_stream, tlv.value_len, key,
                                   request->msg_privacy_parameters, request->msg_authoritative_engine_boots,
                                   request->msg_authoritative_engine_time, algo, SNMP_V3_PRIV_MODE_ENCRYPT));
    }

    if (request->version == SNMP_VERSION_3 && (request->msg_flags & SNMP_V3_AUTH_FLAG))
    {
        u8_t key[20];
        u8_t algo;
        u8_t hmac[20];

        OF_BUILD_EXEC(snmpv3_get_user((char *)request->msg_user_name, &algo, key, NULL, NULL));
        OF_BUILD_EXEC(snmp_pbuf_stream_init(&(request->outbound_pbuf_stream),
                                            request->outbound_pbuf, 0, request->outbound_pbuf->tot_len));
        OF_BUILD_EXEC(snmpv3_auth(&request->outbound_pbuf_stream, frame_size + outbound_padding, key, algo, hmac));

        MEMCPY(request->msg_authentication_parameters, hmac, SNMP_V3_MAX_AUTH_PARAM_LENGTH);
        OF_BUILD_EXEC(snmp_pbuf_stream_init(&request->outbound_pbuf_stream,
                                            request->outbound_pbuf, 0, request->outbound_pbuf->tot_len));
        OF_BUILD_EXEC(snmp_pbuf_stream_seek_abs(&request->outbound_pbuf_stream,
                                                request->outbound_msg_authentication_parameters_offset));

        SNMP_ASN1_SET_TLV_PARAMS(tlv, SNMP_ASN1_TYPE_OCTET_STRING, 1, SNMP_V3_MAX_AUTH_PARAM_LENGTH);
        OF_BUILD_EXEC(snmp_ans1_enc_tlv(&request->outbound_pbuf_stream, &tlv));
        OF_BUILD_EXEC(snmp_asn1_enc_raw(&request->outbound_pbuf_stream,
                                        request->msg_authentication_parameters, SNMP_V3_MAX_AUTH_PARAM_LENGTH));
    }
#endif

    pbuf_realloc(request->outbound_pbuf, frame_size + outbound_padding);

    snmp_stats.outgetresponses++;
    snmp_stats.outpkts++;

    return ERR_OK;
}

static void
snmp_execute_write_callbacks(struct snmp_request *request)
{
    struct snmp_varbind_enumerator inbound_varbind_enumerator;
    struct snmp_varbind vb;

    snmp_vb_enumerator_init(&inbound_varbind_enumerator, request->inbound_pbuf, request->inbound_varbind_offset, request->inbound_varbind_len);
    vb.value = NULL; /* do NOT decode value (we enumerate outbound buffer here, so all varbinds have values assigned, which we don't need here) */

    while (snmp_vb_enumerator_get_next(&inbound_varbind_enumerator, &vb) == SNMP_VB_ENUMERATOR_ERR_OK)
    {
        snmp_write_callback(vb.oid.id, vb.oid.len, snmp_write_callback_arg);
    }
}


/* ----------------------------------------------------------------------- */
/* VarBind enumerator methods */
/* ----------------------------------------------------------------------- */

void
snmp_vb_enumerator_init(struct snmp_varbind_enumerator *enumerator, struct pbuf *p, u16_t offset, u16_t length)
{
    snmp_pbuf_stream_init(&(enumerator->pbuf_stream), p, offset, length);
    enumerator->varbind_count = 0;
}

#define VB_PARSE_EXEC(code)   PARSE_EXEC(code, SNMP_VB_ENUMERATOR_ERR_ASN1ERROR)
#define VB_PARSE_ASSERT(code) PARSE_ASSERT(code, SNMP_VB_ENUMERATOR_ERR_ASN1ERROR)

snmp_vb_enumerator_err_t
snmp_vb_enumerator_get_next(struct snmp_varbind_enumerator *enumerator, struct snmp_varbind *varbind)
{
    struct snmp_asn1_tlv tlv;
    u16_t  varbind_len;
    err_t  err;

    if (enumerator->pbuf_stream.length == 0)
    {
        return SNMP_VB_ENUMERATOR_ERR_EOVB;
    }
    enumerator->varbind_count++;

    /* decode varbind itself (parent container of a varbind) */
    VB_PARSE_EXEC(snmp_asn1_dec_tlv(&(enumerator->pbuf_stream), &tlv));
    VB_PARSE_ASSERT((tlv.type == SNMP_ASN1_TYPE_SEQUENCE) && (tlv.value_len <= enumerator->pbuf_stream.length));
    varbind_len = tlv.value_len;

    /* decode varbind name (object id) */
    VB_PARSE_EXEC(snmp_asn1_dec_tlv(&(enumerator->pbuf_stream), &tlv));
    VB_PARSE_ASSERT((tlv.type == SNMP_ASN1_TYPE_OBJECT_ID) && (SNMP_ASN1_TLV_LENGTH(tlv) < varbind_len) && (tlv.value_len < enumerator->pbuf_stream.length));

    VB_PARSE_EXEC(snmp_asn1_dec_oid(&(enumerator->pbuf_stream), tlv.value_len, varbind->oid.id, &(varbind->oid.len), SNMP_MAX_OBJ_ID_LEN));
    varbind_len -= SNMP_ASN1_TLV_LENGTH(tlv);

    /* decode varbind value (object id) */
    VB_PARSE_EXEC(snmp_asn1_dec_tlv(&(enumerator->pbuf_stream), &tlv));
    VB_PARSE_ASSERT((SNMP_ASN1_TLV_LENGTH(tlv) == varbind_len) && (tlv.value_len <= enumerator->pbuf_stream.length));
    varbind->type = tlv.type;

    /* shall the value be decoded ? */
    if (varbind->value != NULL)
    {
        switch (varbind->type)
        {
        case SNMP_ASN1_TYPE_INTEGER:
            VB_PARSE_EXEC(snmp_asn1_dec_s32t(&(enumerator->pbuf_stream), tlv.value_len, (s32_t *)varbind->value));
            varbind->value_len = sizeof(s32_t *);
            break;
        case SNMP_ASN1_TYPE_COUNTER:
        case SNMP_ASN1_TYPE_GAUGE:
        case SNMP_ASN1_TYPE_TIMETICKS:
            VB_PARSE_EXEC(snmp_asn1_dec_u32t(&(enumerator->pbuf_stream), tlv.value_len, (u32_t *)varbind->value));
            varbind->value_len = sizeof(u32_t *);
            break;
        case SNMP_ASN1_TYPE_OCTET_STRING:
        case SNMP_ASN1_TYPE_OPAQUE:
            err = snmp_asn1_dec_raw(&(enumerator->pbuf_stream), tlv.value_len, (u8_t *)varbind->value, &varbind->value_len, SNMP_MAX_VALUE_SIZE);
            if (err == ERR_MEM)
            {
                return SNMP_VB_ENUMERATOR_ERR_INVALIDLENGTH;
            }
            VB_PARSE_ASSERT(err == ERR_OK);
            break;
        case SNMP_ASN1_TYPE_NULL:
            varbind->value_len = 0;
            break;
        case SNMP_ASN1_TYPE_OBJECT_ID:
            /* misuse tlv.length_len as OID_length transporter */
            err = snmp_asn1_dec_oid(&(enumerator->pbuf_stream), tlv.value_len, (u32_t *)varbind->value, &tlv.length_len, SNMP_MAX_OBJ_ID_LEN);
            if (err == ERR_MEM)
            {
                return SNMP_VB_ENUMERATOR_ERR_INVALIDLENGTH;
            }
            VB_PARSE_ASSERT(err == ERR_OK);
            varbind->value_len = tlv.length_len * sizeof(u32_t);
            break;
        case SNMP_ASN1_TYPE_IPADDR:
            if (tlv.value_len == 4)
            {
                /* must be exactly 4 octets! */
                VB_PARSE_EXEC(snmp_asn1_dec_raw(&(enumerator->pbuf_stream), tlv.value_len, (u8_t *)varbind->value, &varbind->value_len, SNMP_MAX_VALUE_SIZE));
            }
            else
            {
                VB_PARSE_ASSERT(0);
            }
            break;
        case SNMP_ASN1_TYPE_COUNTER64:
            VB_PARSE_EXEC(snmp_asn1_dec_u64t(&(enumerator->pbuf_stream), tlv.value_len, (u32_t *)varbind->value));
            varbind->value_len = 2 * sizeof(u32_t *);
            break;
        default:
            VB_PARSE_ASSERT(0);
            break;
        }
    }
    else
    {
        snmp_pbuf_stream_seek(&(enumerator->pbuf_stream), tlv.value_len);
        varbind->value_len = tlv.value_len;
    }

    return SNMP_VB_ENUMERATOR_ERR_OK;
}

#endif /* LWIP_SNMP */
